Is Life Inevitable ?

[syzygy42]

Above and beyond specific chemical reactions, there are some purely theoretical based on the underlying structure of the chemical network. Kauffman's autocatalytic sets, mentioned above, is one such example, but there are many others. Unfortunately, as Athel Cornish-Bowden points out, most of the researchers in the field have been academic loners, rarely citing each other's work. An excellent review of the history of this subject area is From L'Homme Machine to metabolic closure: Steps towards understanding life by Letelier, Cardenas and Cornish-Bowden.

In brief, these authors give a short history of the underlying metaphors used to develop and frame our understanding of how life works: from late 18th century of a mechanical understanding (think clock), through molecular biology, and finally to systems biology. One central theme underlying almost all of the various "modern" theories is that of metabolic closure, i.e. all of the essential components of an organism are required for the synthesis of all of the other essential components and itself. This self-referential property of living systems is to my mind the thorniest problem confronting theoretical biology (shades of GEB).

The following is a brief synopsis of several theories being bandied about. One of the problems with reading the different authors is that a coherent language of this subject has yet to evolve. Thus, the authors use different words for the same concept and the same words for different concepts. Often these words are different from how biologists use them. This is not meant as a critisism of the authors, since they come from very diverse backgrounds.

(M,R) systems - This theory was developed by Robert Rosen, a mathematician who had a life-long interest in biology. As a graduate student, he and Nicolas Rashevsky developed an approach they referred to as relational biology emphasizing topology over molecular details. From this, Rosen went on to develop his (M,R) systems theory. His theory was developed within the mathematical confines of category theory and was thus beyond the comprehension of most biologists. Recently, Cornish-Bowden and coworkers have translated the essential arguments into set theory

Originally, the "M" stood for metabolism and the "R" stood for repair. Since these words have specific meanings in current molecular biology, C-B has suggested replacement as a more appropriate word that is closer to the underlying meaning within the system. Metabolism is represented as a mapping of substrates to products in the broadest sense, i.e. every molecule within a living organism is a product of metabolism. A subset of these products act as catalysts that are responsible for all of the reactions (mappings). Replacement is more abstract. It is a subset of catalysts that are required for the replacement of catalysts lost due to degradation, inactivation, or dilution because of growth.

Translation of these concepts to biological systems is a daunting task since even the simplest extant systems are extremely complex. A few toy models have been developed to aid in the understanding of these concepts. Regardless, one key aspect from the study of these systems is that they are not hierarchical. Hierarchy is important for understanding subsystems (e.g., gene expression), but for origin of life theories, one can never lose sight of the properties of the whole system.

Autopoiesis - This theory has a rather circuitous route of development. The original theory was developed by Humberto Maturana in the late 1960s and early 1970s. It was developed from using cybernetics to understand the functioning of the brain (modelled after a computer) and an attempt to model the Chilean economy. Maturana came to the conclusion that the brain/computer metaphor was seriously flawed due to the strict input -> output nature of the computer metaphor. Instead, he hypothesized that systems involved in perception/response were always active and constituted a continuous loop. Although different in origin, autopoiesis has many of the same concepts and properties as (M,R) systems.

The chemoton - This is a system of a model organism proposed by Tibor Ganti and published mostly in Hungarian, though an English book was published in 2003, The Principles of Life (Oxford Univ Press). This model provides an outline of a fully functional cell with the incorporation of metabolic, informational, and structural systems. I have not read the book, but Letelier et al. point out that catalytic cycles are a major feature this model.

The hypercycle - Extant organisms have large genomes that specify enzymes that replicate and repair the genome. Obviously, early in the development of life, the enzymes and genomes were much smaller and simpler. The problem with this is that replicating a genome of a decent size requires a low enough error rate to avoid error catastrophy. Maynard Smith and Szathmary coined this Eigen's paradox. Manferd Eigen and Peter Schuster proposed a hypercycle to deal with this problem. This cycle consists of a set of RNA molecules each specifying the synthesis of an enzyme that replicated an RNA molecule different from the one that encoded it. Their analysis suggested that different hypercycle quasispecies could occupy the same space and evolve by Darwinian selection.

Autocatalytic sets - Freeman Dyson and Stuart Kauffman asked the question of what properties were necessary for self organization. Kauffman has pursued this line of reasoning since the mid 1980s. He has always used quirky terms, and in his book The Origins of Order, he refers to this self organization as the Fourth Law of Thermodynamics. I read the book when it first came out, and if one looks more at his arguments than his language, there are many interesting concepts to be examined, from cellular automata to rugged landscapes to gradients in morphogenesis. The basic concept of autocatalytic sets is one of metabolic closure where each metabolite is synthesized by another metabolite in the system. His basic argument is that given enough variety in molecules, some of them will catalyze the formation of other molecules, which in turn catalyze more molecules. From this variety, an autocatalytic set can (will?) emerge and "replicate" itself from the available materials.

Recently Hordijk and Steel have developed Reflexive autocatalytic sets (RAF) to provide a more solid foundation for studying autocatalytic sets. One important contribution is the development of an algorithm to generate these sets, making them amenable to analysis on a computer.

Metabiology - A relative latecomer (not mentioned in this review) is Gregory Chaitin, a mathematician, recently published a book, "Proving Darwin: Making Biology Mathematical". It's on my reading list, but from what I can gather it is about studies that grew out of evolution of LISP programs. Could be an interesting read.

None of the above models are complete and each have their deficiencies/problems as outlined in more detail in the review. Yet, each has contributed valuable concepts and ideas. I must admit that I have been strongly influenced by the writings of Cornish-Bowden. I first encountered his work in basic biochemistry and learned Metabolic Control Analysis from his writings (along with a bunch of others). I look forward to getting the new edition of his textbook, Fundamentals of Enzyme Kinetics, which is now affordable ($63 as opposed to the previous edition at ~$500).

For those who want to read more, the bibliography of the Letelier et al. paper is extensive. For those not familiar with finding non-paywalled papers, Google Scholar is a great resource with links to ungated pdf versions, plus a whole lot more.

Obviously, there is much more on the wet bench side of things along with more specific proposals involving biochemical and organic reactions.

Cheers

[Paul Wally]

Well, what I'm trying to say here, (even though I'm trying to steer away from the uncertainty of abiogenesis), is that there seems to be an implied assumption that pre-biotic chemical reactions might be dominated by equilibrium thermodynamic behaviours, where the driving forces are balanced so no state changes occur, unless the system is acted upon externally. In such equilibrium thermodynamics, any subsequent state changes, can be predicted by formula calculations.

I would limit my assumptions to fundamental physics and chemistry until/if it becomes necessary to revise those assumptions. Thermodynamics (equilibrium and non-equilibrium) I take to be defined on macroscopic observables like temperature, pressure, entropy (correct me if I'm wrong). So what happens now is that non-equilibrium thermodynamics cannot be explained by equilibrium thermodynamics. I think both macroscopic classes of phenomena still follow from the same underlying physical and chemical mechanisms, it's just that for the non-equilibrium phenomena it becomes difficult to develop a macroscopic phenomenological theory of the behaviour.

However there is an entire class of non-equilibrium thermodynamical chemical systems, which result in non-linear chemical 'oscillators' (eg: the Belousov-Zhabotinsky reaction). The macroscopic behaviours of these reactions also mimic the growth patterns of certain amoeba colonies at different spatial and temporal scales (see the Wiki article).

I had a look at this article and also at some non-equilibrium stuff. What caught my attention was the computer simulation depicted on the side. The fact that it can be simulated suggests that we know the microscopic mechanisms responsible for these kinds of phenomena, we just don't know exactly how to predict it in an analytical way.

We view evolution as a distinct dynamic process which we normally think of as only pertaining to life from self-replicating cells onwards, but the process itself, clearly exists in inert chemical reactions as well.

I would define self-replication and evolvability as minimum requirements for biological evolution. The Belousov-Zhabotinsky reaction is an example of complex pattern formation, but is there anything identifiable as self-replication in there? If there is, then that would be very interesting.

So, how might this class of non-linear, far from equilibrium, naturally oscillating chemical phenomena, have influenced the formation pre-biotic chemistry ? How prevalent (or uncommon) might such a class of reactions have been, in pre-biotic environments ? Could it have influenced what eventually became life? What effect would such a process have on the predictability of the emergence of complex life elsewhere? More specifically, what effect might it have on the predictability of the phase trajectory assumptions mentioned in the Longo paper ?
(Some rhetorical questions here .. hopefully only to demonstrate that unexpected outcomes are at least quite possible, when it comes to certain chemical environments).

That similar kinds of phenomena are found in different physical scenarios and simple computer simulations, suggests to me that it shouldn't be uncommon, but more rigorous proof is of course required. I do want to add though, that unexpected outcomes we find in pure mathematics also even though we have the rules or axioms of the system clearly defined.

[Selfsim]

I think both macroscopic classes of phenomena still follow from the same underlying physical and chemical mechanisms, it's just that for the non-equilibrium phenomena it becomes difficult to develop a macroscopic phenomenological theory of the behaviour.

I think the main point behind such phenomena is that we know such reactions will produce a kind of pattern, but we can't predict the exact shapes.

Along the same lines, the question which some of the theories in syzygy42's post are attempting to grapple with is: "Can nature's ability to turn simplicity into complexity in such an unpredictable way, explain why life exists ?"

I had a look at this article and also at some non-equilibrium stuff. What caught my attention was the computer simulation depicted on the side. The fact that it can be simulated suggests that we know the microscopic mechanisms responsible for these kinds of phenomena, we just don't know exactly how to predict it in an analytical way.

Meaning that the phenomenon itself, is inherently unpredictable, at certain scales.

The big question is: "At which scales ?"

Unless there is direct empirical evidence at the exo-planetary scale, attempts at phenomenological theories will have no predictive validity in the physical universe … ie: inherently unpredictable … not 'likely'.

I would define self-replication and evolvability as minimum requirements for biological evolution. The Belousov-Zhabotinsky reaction is an example of complex pattern formation, but is there anything identifiable as self-replication in there? If there is, then that would be very interesting.

Well, I think the patterns exhibit fractal dimensionality. (A fractal being generated by simple rules repeated over and over again .. recursive in nature .. incorporating feedback, and self-similarity). Where, and when, a particular self-similar feature will recur, (or even if it recurs), is unpredictable.

What if life on Earth is one instance of such a feature ? The next instance would be unpredictable, and not necessarily inevitable, until we have evidence of the scales of self-similarity, both spatially and temporally.

That similar kinds of phenomena are found in different physical scenarios and simple computer simulations, suggests to me that it shouldn't be uncommon, but more rigorous proof is of course required. I do want to add though, that unexpected outcomes we find in pure mathematics also even though we have the rules or axioms of the system clearly defined.

There is plenty of evidence that such processes in nature are common.
The unexpected outcomes (seemingly, in spite of the rules and axioms we use to describe them), is the nature of Chaos. It all somehow fits into the Standard Physical (and Chemical) Laws. It can fit into those laws without necessarily being predictable. As a matter of fact, there is plenty of abundant evidence that many natural systems do exactly this. Predictability and inevitability are scale dependent. The concept of the "Infinite Universe" is the only theoretical basis I can think of, which would make all this inevitable (and the observable universe isn't infinite).

Regards

[Selfsim]

Such an "implied assumption" may have been there once. However, recent work on abiogenesis takes energy gradients and energy flows to be a basic ingredient in the process. Such a gradient is the state of affairs opposite to equilibrium. I'd suggest (once again) that you have a look at James Trefil et al The Origin of Life in the journal American Scientist.

Ok .. I'll have a read and get back shortly. As a precursor, the question is already set in my mind as to whether the assumptions of symmetry get thrown out when incorporating such gradients. What is the impact on predictability ?

More later.

As promised, I've had a read through this article.
Overall, I find that its probably almost exactly what Longo et al are saying is the very kind of formulaic, reductionist thinking, which they criticise as being inappropriate as far biology reasoning is concerned. (Note this statement is my attempt at coming from the Longo perspective .. but is not an attempt at pushing my own personal views).

I also notice that it appeared in April 2009, whereas the Longo et al paper was dated Jan 2012 (~3 years later).

I must admit that I also feel very uncomfortable with statements such as:

Current research into this foundational question now centers on the fact that the chemical substrate of living systems is much more complex than that of simple physical systems that have been examined so far. One important new direction of research involves the development of small-molecule catalysts in increasingly complex cooperative networks. The hope is that when a full theory is available, we will see the formation of life as an inevitable outcome of basic thermodynamics, like the freezing of ice cubes or the formation of magnets.

Sort of putting the cart before the horse, isn't this ?

Ie: .. why is there a hope from the outset that: "we will see the formation of life as an inevitable outcome of basic thermodynamics" ???
By their own words, this seems to be a classic case of building a story based on a reductionist world view, then propping it up by carefully contrived lab experiments, then calling it a 'theory'?

In a larger sense, however, the future of the experimental program associated with the Metabolism First philosophy is tied to the development of the appropriate theory, guided by experimental results. The hope is that the interplay of theory and experiment, so familiar to historians of science, will produce a theory that illuminates the physical principles that led to the development of life and, hence, give us the ability to re-create life in our laboratories.

Well, with such a heavily biased motivating influence behind the development of such a 'theory', about the only way it could be accepted, would be if it did re-create life in the laboratories !

Notice how a philosophy is deliberately tied to the development of an 'appropriate theory' ?!!

Does no-one else see how biased this approach is ? Where are the steps for ensuring that they don't just end up with the answer they were looking for all along ? Seems to me, these have been deliberately excluded ...

More back-to-front (circular) reasoning:

Assuming the experimental and theoretical programs outlined above work out well, our picture of life as a robust, inevitable outcome of certain geochemical processes will be on firm footing. Who knows? Maybe then someone will write a book titled Necessity, Not Chance.

Once again, their 'picture of life' shall be reinforced by the story and evidence they deliberately select ??
Then, the story they're creating is for the purpose of writing books, eh ?
(As distinct from an attempt at investigative science ?).

Honestly, this entire article (and, perhaps, their 'research' program(?) ), is based on just what they say its based on ... ie: "our picture of life as a robust, inevitable outcome of certain geochemical processes".

I can now see why Longo et al are writing papers like they have ! (Not that theirs is necessarily much different, mind you).
And this piece of literature also reinforces Letelier/Cardenas/Cornish-Bowden's assertions that: 'most of the researchers in the field have been academic loners, rarely citing each other's work', (as outlined in syzygy42's post #31).

Still, the content of what they present, in isolation, seems quite sound, so I'd regard the Trefil et al article, as yet another one to add to the Letelier list, presented by syzygy42.

… Gee, all these 'theories' … and no way to distinguish a preferred one over any of the others, (other than via a philosophically based worldview), eh ?

.. What we need is some empirical evidence … you know, like a local exo-life discovery ?!

[Selfsim]

Above and beyond specific chemical reactions there are some purely theoretical based on the underlying structure of the chemical network. Kauffman's autocatalytic sets, mentioned above, is one such example, but there are many others …. {big snip} …
… From L'Homme Machine to metabolic closure: Steps towards understanding life
…
(M,R) systems … Autopoiesis … The chemoton … The hypercycle … Autocatalytic sets … Metabiology …

None of the above models are complete and each have their deficiencies/problems as outlined in more detail in the review.

Hi syzygy;

… A very useful article … capturing a broad spectrum of the ideas being worked on.

Many thanks for the 'heads-up'.

Certainly highlights the unpredictability of exo-life issue, especially if the present theoretical status is undecided on which variant of these, reflects the as yet, undiscovered reality.

One central theme underlying almost all of the various "modern" theories is that of metabolic closure, i.e. all of the essential components of an organism are required for the synthesis of all of the other essential components and itself. This self-referential property of living systems is to my mind the thorniest problem confronting theoretical biology (shades of GEB).

.. and I'm not sure whether any of these theories is ultimately ever going to crack that problem ..
In the meantime, the whole decision landscape is dominated by philosophically based opinion … which is certainly no scientific basis for assuming 'inevitability'.

Cheers

[Paul Wally]

Unless there is direct empirical evidence at the exo-planetary scale, attempts at phenomenological theories will have no predictive validity in the physical universe … ie: inherently unpredictable … not 'likely'.

The three concepts that you're using: "inherentness", "unpredictability" and "likelihood", do not necessarily go together. In other words, a phenomenon can be unpredictable without being inherently unpredictable, and a phenomenon can be inherently unpredictable and yet be highly likely. In this case its possible that the emergence of life is inherently unpredictable and yet highly likely. You see, unpredictability just means that it's random, not that it's necessarily unlikely. Anyway, to get back to "inherent unpredictability" claim; since we don't yet understand the process of how life emerges how is it that you can know that the emergence of life is inherently unpredictable? Maybe it isn't, and we just don't know it yet.

Well, I think the patterns exhibit fractal dimensionality. (A fractal being generated by simple rules repeated over and over again .. recursive in nature .. incorporating feedback, and self-similarity). Where, and when, a particular self-similar feature will recur, (or even if it recurs), is unpredictable.

Fractal patterns are not exactly what I mean by self-replication. With self-replication I mean something making an exact copy of itself, and not a smaller copy of itself still attached to itself. The copy must also be capable of making a copy of itself, and so forth. Self-replication then leads to population growth. Now, if there is some variability in the self-replication process, that makes for variety in the population and that's where natural selection starts coming into the picture. So, in this understanding, biological evolution cannot start before there is both self-replication and variability.

What if life on Earth is one instance of such a feature ?

Life on Earth is one instance of a very general kind of phenomenon, that is self-replication and evolvability, but I wouldn't call these "features" really. A feature is something unique, whereas this phenomenon is of a more general kind.

The next instance would be unpredictable, and not necessarily inevitable, until we have evidence of the scales of self-similarity, both spatially and temporally.

I don't think there is much that needs to be similar, other than the minimum requirements of self-replication and evolvability. Evolution takes care of the rest. I'm not sure I understand what you mean by "evidence of the scales of self-similarity"; what would such evidence look like?

There is plenty of evidence that such processes in nature are common.

Now if such processes are common in nature, why would the emergence of life be uncommon, or am I missing something here?

The unexpected outcomes (seemingly, in spite of the rules and axioms we use to describe them), is the nature of Chaos.

Well, without the rules and axioms there is no chaos theory and thus no "nature of Chaos" to talk about. Chaos is a mathematical concept.

It all somehow fits into the Standard Physical (and Chemical) Laws. It can fit into those laws without necessarily being predictable.

Chaos doesn't just somehow fit, it follows as an implicit possibility of these laws.

Predictability and inevitability are scale dependent.

Could you please provide an example illustrating the meaning of the above statement?

The concept of the "Infinite Universe" is the only theoretical basis I can think of, which would make all this inevitable (and the observable universe isn't infinite).

... hence exolife is not inevitable? But what does this conclusion mean? Suppose we knew for a fact that the universe is teeming with life, how would the concept of "non-inevitability of life" apply in that case?

[Selfsim]

Unless there is direct empirical evidence at the exo-planetary scale, attempts at phenomenological theories will have no predictive validity in the physical universe … ie: inherently unpredictable … not 'likely'.

Anyway, to get back to "inherent unpredictability" claim; since we don't yet understand the process of how life emerges how is it that you can know that the emergence of life is inherently unpredictable? Maybe it isn't, and we just don't know it yet.

i) We don't know the process of how life emerges.
ii) The theory is incomplete. (In this case, lacking in physical evidence).
iii) Prediction requires a theory.
iv) Predictability is not implied.

I would define self-replication and evolvability as minimum requirements for biological evolution. The Belousov-Zhabotinsky reaction is an example of complex pattern formation, but is there anything identifiable as self-replication in there? If there is, then that would be very interesting.

Well, I think the patterns exhibit fractal dimensionality. (A fractal being generated by simple rules repeated over and over again .. recursive in nature .. incorporating feedback, and self-similarity). Where, and when, a particular self-similar feature will recur, (or even if it recurs), is unpredictable.

Fractal patterns are not exactly what I mean by self-replication. With self-replication I mean something making an exact copy of itself, and not a smaller copy of itself still attached to itself. The copy must also be capable of making a copy of itself, and so forth.

A fractal pattern can form as a result of self-replication. In fractals, interestingly, many sequences of output points of an iterative process, do not converge to a finite quantity, and 'escape' to infinity. (I don't know for sure, but I think there may be more that do this, than converge, depending on the fractal expression, and assuming a large, but finite bounded iteration space .. a bit like the observable universe space, but I am not certain of this .. its an interesting question, though). So, if life on Earth were to represent the set of non-escaping sequences resulting from a starting point, then there would be many (more?) escaping sequences resulting from the overall interative process .. and they may not result in viable lifeforms.
This is really pure conjecture/fantasy, (and only for illustrative purposes .. to get the feeling for the permutation space outside of life-as-we-know-it), but if the pattern of life distribution throughout the universe is generated by a natural iterative process, then non-viable outcomes would also result. The question remains .. what is the scale of the boundary which might separate viable and non viable outcomes … and we don't know this. Thinking of it all in fractal terms at least forces us to think simultaneously, about both sides of the 'likely/unlikely' biological coin, maintaining some semblance of balance about this, as well as reminding us about the detailed unpredictability over-riding it all.

Well, I think the patterns exhibit fractal dimensionality. (A fractal being generated by simple rules repeated over and over again .. recursive in nature .. incorporating feedback, and self-similarity). Where, and when, a particular self-similar feature will recur, (or even if it recurs), is unpredictable.

What if life on Earth is one instance of such a feature ? The next instance would be unpredictable, and not necessarily inevitable, until we have evidence of the scales of self-similarity, both spatially and temporally.

Life on Earth is one instance of a very general kind of phenomenon, that is self-replication and evolvability, but I wouldn't call these "features" really. A feature is something unique, whereas this phenomenon is of a more general kind.

.. and can be abstracted and found to mimic non-linear recursion .. along with all its implications. I think this is a more fundamental, generalised natural process than say, self-replication or evolvability, (which is specific to the progress of biology), as it can be applied in more fundamentally based, (inorganic), processes such as fusion in a star, coelescence of gases and dust, accretion, etc.

I don't think there is much that needs to be similar, other than the minimum requirements of self-replication and evolvability. Evolution takes care of the rest. I'm not sure I understand what you mean by "evidence of the scales of self-similarity"; what would such evidence look like?

Other instances of exo-life at measurable spatial distances and temporal scales.

Now if such processes are common in nature, why would the emergence of life be uncommon, or am I missing something here?

I'm not sure it would be uncommon. (I'm not saying this .. there's no direct evidence). But thinking about it from this paradigm, at least follows roughly one established by biological behaviours. Following my fractal 'fantasy' above, I wonder how many sets are discarded (or escape) in a finite 'run' of say a Mandelbrot Set algorithm ? (They're usually the coloured pixels, I think .. ?)

Well, without the rules and axioms there is no chaos theory and thus no "nature of Chaos" to talk about. Chaos is a mathematical concept.

I've seen you mention this elsewhere. Chaos is intrinsic in nature. Mathematics is the language used to model it. 'Tis not a purely theoretical abstraction emerging from some mathematical formula, which has no physical significance !

Chaos doesn't just somehow fit, it follows as an implicit possibility of these laws.

I'd say Chaos is an explicit outcome of natural laws which results in unpredictability at certain scales.

Predictability and inevitability are scale dependent.

Could you please provide an example illustrating the meaning of the above statement?

Lets see, now ... hmm .. how about ...

i) Death of any human being is inevitable on a scale of say, five hundred years. Death of any human being is not inevitable on a scale of say, one month.

ii) The orbital period of Halley's comet over the last 3 centuries, can be predicted to be between 75 and 76 years. Over the last 2250 years however, its period can be predicted to be between 74 and 79 years.

The concept of the "Infinite Universe" is the only theoretical basis I can think of, which would make all this inevitable (and the observable universe isn't infinite).

... hence exolife is not inevitable?

Nope ... that's a different statement .. and its not what I'm saying. Inevitability is unknown. (What I'm saying may have come across ambiguously, due to this text medium ??)

The concept of the "Infinite Universe" is the only theoretical basis I can think of, which would make all this inevitable (and the observable universe isn't infinite).

But what does this conclusion mean? Suppose we knew for a fact that the universe is teeming with life, how would the concept of "non-inevitability of life" apply in that case?

The point is: we don't know this.

Regards

[Hlafordlaes]

Barring mythical causes, that abiogenesis happened either implies that it happens, or that it was a singularity. I think it happens. There is no indication that the physics and chemistry on our planet is rare or exceptional, containing as it does that mix of elements and conditions one might expect from known planetary formation. To argue it as a singularity seems to imply we need to find something authentically special about local conditions, doesn't it?

IOW, if nature tries the same experiment with the same or similar soup elsewhere, why should we expect different results? Is nature crazy?

[Selfsim]

Barring mythical causes, that abiogenesis happened either implies that it happens, or that it was a singularity. I think it happens.

It must have happened. How else could life exist ? Whether we call the event 'abiogenesis' or, 'a singularity', is just semantics.

There is no indication that the physics and chemistry on our planet is rare or exceptional, containing as it does that mix of elements and conditions one might expect from known planetary formation. To argue it as a singularity seems to imply we need to find something authentically special about local conditions, doesn't it?

Ignoring any particular meaning associated with the term 'singularity' (see above comment), ….. No !…. Not at all !

What could be said is that it could be a perfectly natural outcome .. with absolutely nothing special about local conditions, needing to be shown.

For example, try on:
"It just happened to have happened here .. and we showed up later, to notice that it happened here". (The Anthropic Principle).

The perspective you mention (which should be equally valid, although not necessary), is caused by a strong interpretation of the Copernican Principle, (or more broadly .. the Cosmological Principle) .. but, "it ain't the only Principle in town" !

IOW, if nature tries the same experiment with the same or similar soup elsewhere, why should we expect different results? Is nature crazy?

Whilst there is no compelling evidence to suggest that abiogenesis is necessarily a Chaotic phenomenon, it is equally possible that if it was, no two outcomes would necessarily be the same because either:

i) no two initial (pre-abiogenesis) conditions might be identical or;
ii) we have no way of knowing what those precise original (pre-abiogenesis) conditions were, and hence we have no way of knowing that a another re-run of the same process would necessarily result in a viable emergent lifeform.

This is Chaos Theory's 'sensitive dependence on initial conditions', and is the basic conclusion of Edward Lorenz's work on non-linear dynamics, (and has mathematical proof underpinning it): even if one knows the initial conditions quite precisely, the error in specifying the initial condition rapidly grows, so that after even a short time, one cannot predict the details of the outcome. And any of these 'details', could easily be critical for life to become viable (or non-viable).

I have no particular interest in pushing the idea, because there is no physical evidence that the abiogenesis event ever happened this way, but it certainly is possible in theory, and many presently functioning biological systems, (and Evolution), behave in just this way. The 'unknown' status of (i) how metabolic closure occurs and; (ii) the self-referential property of living systems, allows for this possibility in abiogenesis theory.

If it is possible in theory, then 'predictability' and 'inevitability' are not necessarily assured. Personally, I'd still say both of these aspects are still 'unknown', (for all the above reasons).

Regards

[Colin Robinson]

Barring mythical causes, that abiogenesis happened either implies that it happens, or that it was a singularity. I think it happens. There is no indication that the physics and chemistry on our planet is rare or exceptional, containing as it does that mix of elements and conditions one might expect from known planetary formation. To argue it as a singularity seems to imply we need to find something authentically special about local conditions, doesn't it?

IOW, if nature tries the same experiment with the same or similar soup elsewhere, why should we expect different results? Is nature crazy?

Whether the results would be different or not, is not necessarily an either/or question.

When water vapour condenses into snow crystals, every crystal is different, though they are also structurally similar. The process that led to abiogenesis was presumably more complex than crystallization of snow. Perhaps that means greater diversity of possible results?

Isn't it conceivable that "soups" on other worlds might result in intricate chemical systems and physical structures which we will find difficult to classify either as living or as non-living?

[Colin Robinson]

This is Chaos Theory's 'sensitive dependence on initial conditions', and is the basic conclusion of Edward Lorenz's work on non-linear dynamics, (and has mathematical proof underpinning it): even if one knows the initial conditions quite precisely, the error in specifying the initial condition rapidly grows, so that after even a short time, one cannot predict the details of the outcome.

Edward Lorenz was a meteorologist.

No doubt he was right that some of the details of meteorological systems can't be predicted much in advance. But does that mean all bets are off, that nothing can be said about what is likely to happen?

E.g. It may be impossible to predict exactly when and where the next tropical cyclone is going to form. On the other hand, it has long been known that tropical cyclones tend to form at a particular range of latitudes (which is why they are called "tropical", after all) and at particular times of year…

[Selfsim]

Edward Lorenz was a meteorologist.

No doubt he was right that some of the details of meteorological systems can't be predicted much in advance. But does that mean all bets are off, that nothing can be said about what is likely to happen?

What Lorenz was, or wasn't, is not relevant. What he, and many others discovered in theory, is.

Unpredictability at certain scales in non-linear Chaotic Systems in nature, is a mathematical certainty.

E.g. It may be impossible to predict exactly when and where the next tropical cyclone is going to form. On the other hand, it has long been known that tropical cyclones tend to form at a particular range of latitudes (which is why they are called "tropical", after all) and at particular times of year…

As I have said numerous times in this thread, (and provided examples thereof), the unpredictability in these systems is spatially and temporally scale dependent. You have cited yet another example.

Regards

[Colin Robinson]

What Lorenz was, or wasn't, is not relevant. What he, and many others discovered in theory, is.

It's relevant because meteorological systems are the classical chaotic systems. If chaos theory is applicable to abiogenesis, that means the processes involved in abiogenesis are in some ways comparable to meteorological processes.

As I have said numerous times in this thread, (and provided examples thereof), the unpredictability in these systems is spatially and temporally scale dependent. You have cited yet another example.

The point I'm interested in is this...

Does a chaotic model of abiogenesis necessarily contradict the hypotheses of Stuart Kauffman and Christian de Duve and James Trefil, all of whom have argued for abiogenesis being a high-probability process?

My example -- formation of tropical cyclones -- suggests to me that a chaotic model does not necessarily contradict their hypotheses.

[Selfsim]

The point I'm interested in is this...

Does a chaotic model of abiogenesis necessarily contradict the hypotheses of Stuart Kauffman and Christian de Duve and James Trefil, all of whom have argued for abiogenesis being a high-probability process?

My example -- formation of tropical cyclones -- suggests to me that a chaotic model does not necessarily contradict their hypotheses.

Ok, as an example, so a quick overview summary of Trefil's hypothesis follows:

We believe this early version of metabolism consisted of a series of simple chemical reactions running without the aid of complex enzymes, via the catalytic action of networks of small molecules, perhaps aided by naturally occurring minerals. If the network generated its own constituents—if it was recursive—it could serve as the core of a self-amplifying chemical system subject to selection. We propose that such a system arose and that much of that early core remains as the universal part of modern biochemistry, the reaction sequences shared by all living beings. Further elaborations would have been added to it as cells formed and came under RNA control, and as organisms specialized as participants in more complex ecosystems.

From my read of that, all of the basic fundamentals of Chaos are incorporated. In his pursuit of closing the thermodynamic pathway, by suggesting the citric acid cycle as a fundamental, (etc), he drills down, (in true reductionist form), to the molecular levels, in order to find a level where he can come up with a hypothetical step-by-step rationale, leading towards what looks like a pre-determined outcome .. ie: an inevitable metabolism first outcome.

As Longo (and Kauffman) argue in their paper however, this approach is very formulaic, whereas what they propose, is less so. Frankly, I think Kauffman is backing both horses. I concur that Kauffman has written extensively from the view which ultimately concludes an inevitable life resultant, following a non-linear, complex systems route. However, I do think that his thinking (relating to inevitability of life), is a purely philosophically based pre-conceived interpretation, which ignores the reality of unpredictability inherent in Chaos Theory. And all this, even though Kauffman is more focused on biological Systems Complexity, (which encompasses Chaos principles, and self-assembly). I mentioned somewhere else, (in response to Cougar, somewhere), that I find Kauffman tends to spend a lot less time on falsification of his hypotheses, than verification, and this is where I was coming from .. ie: the exclusion of the unpredictability component introduced by Chaos inherent in Complexity.

All this comes down to the scales at which one thinks unpredictability and predictability operate in the process.

Also, I think syzgy42's comment about the unknown part of metabolic closure, being 'one of the thorniest problems', might be right on the mark ... and may account for what I think, is some inconsistency in each of these hypotheses.

I haven't looked at de Duve's material from this perspective yet. Have you posted any de Duve links in this thread ? (Apologies if I missed it).

Regards

[Colin Robinson]

Ok, as an example, so a quick overview summary of Trefil's hypothesis follows:
From my read of that, all of the basic fundamentals of Chaos are incorporated. In his pursuit of closing the thermodynamic pathway, by suggesting the citric acid cycle as a fundamental, (etc), he drills down, (in true reductionist form), to the molecular levels, in order to find a level where he can come up with a hypothetical step-by-step rationale, leading towards what looks like a pre-determined outcome .. ie: an inevitable metabolism first outcome.

Re Trefil's suggestion that the citric acid cycle or something like it was a very early, thermodynamically favored precursor to metabolism...

In November 2009, a few months after the Trefil article was published, Marcelo Guzman published laboratory results which showed that most (at least) of the steps in the reductive citric acid cycle (aka the reductive Krebs cycle) can indeed take place with the help of mineral catalysts instead of enzymes.

Summary of Guzman's results in Astrobiology Magazine…

"Guzman and Martin tried to chemically replicate the Krebs cycle – that is, without enzymes playing a role. They experimented with the semi-conducting mineral zinc sulfide as the catalyst. But iron, cadmium and manganese can also be used, says Guzman. Using a “colloidal suspension” (a chemical mixture in which a solid is suspended in a liquid) of zinc sulfide and sodium sulfide and exposing it to UV light, the research team was able to reproduce about 70 percent of the cycle."

As Longo (and Kauffman) argue in their paper however, this approach is very formulaic, whereas what they propose, is less so.

Have you forgotten that Longo's paper is about evolution not abiogenesis? Or, when you say "As Longo (and Kauffman) argue", do you mean something like "it can be argued, by extending Longo's and Kauffman's argument back from the sphere of evolution to the sphere of abiogenesis"?

All this comes down to the scales at which one thinks unpredictability and predictability operate in the process.

Yes, this seems like a crucial question.

I haven't looked at de Duve's material from this perspective yet. Have you posted any de Duve links in this thread ? (Apologies if I missed it).

No, I don't think I have posted anything by de Duve. So here is something now...

Christian de Duve, "The Beginnings of Life on Earth" in American Scientist

Regards

[Paul Wally]

i) We don't know the process of how life emerges.
ii) The theory is incomplete. (In this case, lacking in physical evidence).
iii) Prediction requires a theory.
iv) Predictability is not implied.

I asked how you can know the emergence of life is "inherently unpredictable", with emphasis on "inherently". It may just be unpredictable because we don't yet have
a complete theory, as you say in ii), but that is not a sufficient basis for making the much stronger claim of "inherent unpredictability". What is the theoretical basis for your claim that the emergence of life is inherently unpredictable, given certain conditions?

Just to clarify the concept of "prediction"; there are two interpretations I can think of:
1) Temporal prediction, i.e. predicting the evolution of a process in time.
2) Theoretical prediction, i.e. a theory makes a statement that is not yet empirically confirmed, e.g. General Relativity predicting the bending of starlight near the sun.

It is mainly prediction (2) that is relevant here in the sense that we want a theory "predicting" what the necessary conditions for the emergence of life is. But this is not the same as predicting how any particular process is going to evolve in real time as a function of time. This ties in with what Colin said about tropical cyclones. We cannot predict the emergence of cyclones in real time, but we can theoretically predict the necessary conditions for the emergence of cyclones based on our theoretical understanding of atmospheric dynamics. The same kind of thinking applies to emergence of life where we could have theoretical prediction of emergence of the general phenomenon of life as opposed to predicting the evolution of particular lifeforms as a function of time.

Quote Originally Posted by Paul Wally
I don't think there is much that needs to be similar, other than the minimum requirements of self-replication and evolvability. Evolution takes care of the rest. I'm not sure I understand what you mean by "evidence of the scales of self-similarity"; what would such evidence look like?

Quote Originally Posted by Selfsim
Other instances of exo-life at measurable spatial distances and temporal scales.

That is just too vague. What does "evidence of the scales of self-similarity" in particular look like? You make these vague general statements and they're subject to multiple interpretations, so please clarify.

I've seen you mention this elsewhere. Chaos is intrinsic in nature. Mathematics is the language used to model it. 'Tis not a purely theoretical abstraction emerging from some mathematical formula, which has no physical significance !

Chaos, like circles and parabolas, is a purely mathematical concept. Like circles and parabolas are used to model real world phenomena, so chaos is also used to model real world phenomena. You've got the whole thing backwards.

I'd say Chaos is an explicit outcome of natural laws which results in unpredictability at certain scales.

The natural laws are mathematical formulations of how we think nature behaves in general. Chaos follows implicitly from certain mathematical models based on these formulations. Absolutely no empirical data is required for mathematical equations to imply chaos, i.e. no explicit input is required. The chaotic behaviour follows implicitly from the equations and the equations only; that's the beauty of mathematics!

Lets see, now ... hmm .. how about ...

i) Death of any human being is inevitable on a scale of say, five hundred years. Death of any human being is not inevitable on a scale of say, one month.

ii) The orbital period of Halley's comet over the last 3 centuries, can be predicted to be between 75 and 76 years. Over the last 2250 years however, its period can be predicted to be between 74 and 79 years.

These are examples of temporal prediction. How does your "scale -dependence" concept apply to theoretical predictions (as I explained above)?

Nope ... that's a different statement .. and its not what I'm saying. Inevitability is unknown. (What I'm saying may have come across ambiguously, due to this text medium ??)

Inherent unpredictability is unknown too. Just because we don't know, that doesn't mean we can automatically assume inherent unpredictability.

[Selfsim]

I asked how you can know the emergence of life is "inherently unpredictable", with emphasis on "inherently". It may just be unpredictable because we don't yet have a complete theory, as you say in ii), but that is not a sufficient basis for making the much stronger claim of "inherent unpredictability". What is the theoretical basis for your claim that the emergence of life is inherently unpredictable, given certain conditions?

Paul, I never said that that the emergence of life is inherently unpredictable. What I said was:

Unless there is direct empirical evidence at the exo-planetary scale, attempts at phenomenological theories will have no predictive validity in the physical universe … ie: inherently unpredictable … not 'likely'.

... meaning that the theories themselves, would be incapable of delivering predictions .. which would make them inherently incapable of making predictions. Perhaps I should have said "inherently unpredictive" (??) Science cannot determine whether the emergence of life is able to be predicted, or not. Having made this statement, so long as a class of natural phenomena exists, for which we do have evidence supporting unpredictability, (and it forms part of the incomplete abiogenesis theories), unpredictability cannot be ruled out .. but following this line of argument, basically leads back to a status of 'unknown', as predictability coming from certain purely deterministically based rationale can also not be ruled out, for the same reasons. It should be noted that the chemistry cited in most abiogenesis hypotheses is complex and dependent on a very large number of variables, which do lead to dynamic phase states, which can easily behave chaotically.

Unpredictability may be ruled out however, if philosophical bias is driving the theory .. ie: if the emergence of life is believed to be determinable, from the outset, but this would not be coming from scientific argument.

One thought I've been playing around with lately is that I'm thinking that we can never know in detail, those "certain conditions" you mention above, from Earth's history. If the environment plays a role in the abiogenesis of life, then the abiogenesis is also subject to the same unpredictability in the detail of that environment. No amount of data would allow us to 'postdict' the details of that environment backwards over evolutionary timescales. Given this is the case, then its influence on the details proposed by theories of abiogenesis, is also unpredictable over the same timescale. Fossil records also do not contain the kinds of details, which may be of significance.

Just to clarify the concept of "prediction"; there are two interpretations I can think of:
1) Temporal prediction, i.e. predicting the evolution of a process in time.
2) Theoretical prediction, i.e. a theory makes a statement that is not yet empirically confirmed, e.g. General Relativity predicting the bending of starlight near the sun.

It is mainly prediction (2) that is relevant here in the sense that we want a theory "predicting" what the necessary conditions for the emergence of life is.

If this is the agenda behind the development of an abiogenesis 'theory', then it has started out under an unjustifiable premise (and it seems, a philosophically based agenda). The details of the conditions for the emergence of life are unknown, and unpredictable. So how can one come up with a theory which attempts to predict from an unknowable initial condition ?

But this is not the same as predicting how any particular process is going to evolve in real time as a function of time. This ties in with what Colin said about tropical cyclones. We cannot predict the emergence of cyclones in real time, but we can theoretically predict the necessary conditions for the emergence of cyclones based on our theoretical understanding of atmospheric dynamics.

But you can't predict where, or when, other variables may trigger those 'necessary' conditions ... no matter how much data you accumulate. This is the Butterfly Effect ... if a critical state occurs, the slightest variation in the steady-state 'necessary' conditions may or may not trigger the cyclone. And that trigger (or catalyst) itself, cannot be predicted. Neither can the occurrence of the 'necessary' conditions we know of, so at the scales which matter (of interest), what predictive capability does such a cyclone theory have ?
That cyclones are seasonal and tend to be localised within approximate geographical zones, might also represent the self-similar spatial and temporal scale issues at work. (Yet another example of them, actually). But we only know this happens, because of observational evidence .. not theoretical.

The same kind of thinking applies to emergence of life where we could have theoretical prediction of emergence of the general phenomenon of life as opposed to predicting the evolution of particular lifeforms as a function of time.

Why does 'the same kind of thinking apply to the emergence of life' ?

I don't think there is much that needs to be similar, other than the minimum requirements of self-replication and evolvability. Evolution takes care of the rest. I'm not sure I understand what you mean by "evidence of the scales of self-similarity"; what would such evidence look like?

Other instances of exo-life at measurable spatial distances and temporal scales.

That is just too vague. What does "evidence of the scales of self-similarity" in particular look like? You make these vague general statements and they're subject to multiple interpretations, so please clarify.

Instances of replication (other than Earth) of known biological processes - eg similarity with: the citric cycle for metabolism, enzymatic or mineralogic catalysis, polynucleotide molecules used by Earth-life, glycolysis (or similar) using the same or similar enzymes as earth-life in similar sequences, similar molecular chirality as Earth-life, similar amino acid synthesis aligning with our 'standard' genetic code etc. How specific does it have to get in order to satisfy your definition of not 'vague' ?
Similarity with any one of these details would become a valid data point which could perhaps contribute towards giving more weight to certain abiogenesis theories.

I've seen you mention this elsewhere. Chaos is intrinsic in nature. Mathematics is the language used to model it. 'Tis not a purely theoretical abstraction emerging from some mathematical formula, which has no physical significance !

Chaos, like circles and parabolas, is a purely mathematical concept. Like circles and parabolas are used to model real world phenomena, so chaos is also used to model real world phenomena. You've got the whole thing backwards.

I'd say Chaos is an explicit outcome of natural laws which results in unpredictability at certain scales.

The natural laws are mathematical formulations of how we think nature behaves in general. Chaos follows implicitly from certain mathematical models based on these formulations.
Absolutely no empirical data is required for mathematical equations to imply chaos, i.e. no explicit input is required. The chaotic behaviour follows implicitly from the equations and the equations only; that's the beauty of mathematics!

'Backwards' you reckon eh ?
Admittedly, the whole point of physics is to replace what is happening in the real world, with something that may not actually be happening, but what we can make sense of (ie: theoretical models). Some parts of these models can be confirmed to accurately mimic reality via real-world measurements. As it turns out, some chaos models have been originally developed from real-life observational data (eg: meteorological<=>Lorenz models). Lorenz started out with a simplified model for thermal fluid convection but it was then demonstrated that these were the equations of motion of a waterwheel. The waterwheel was built, and demonstrated convincingly the reality of the chaos phenomenon. The subsequent discoveries about sensitivity to initial conditions, then came from mathematical analysis of those models, but the original data, (ie: before it was mapped into deterministic mathematical formulae), came originally from real-world observational measurements of the phenomena and was confirmed in the lab by the waterwheel behaviours.

Having said this, the mathematics of chaos theory is deterministic, but in mathematically modelled chaos systems, as it turns out, determinism is one of the things which doesn't map in the opposite direction .. ie: back across to the real-world.

In general, this is not so surprising ... for example, the failure of the deterministic components to map back into the macroscopic real world behaviours is exhibited in quantum mechanics ... (like the two slit experiments). So here, we have other real-world examples of the same non-mappability of deterministic functions.

Anyway, when there is chaos, it is also clear that we definitely can't say that the model outcomes are deterministic, in spite of them being generated by formulae which describe a deterministic model. The solutions to a chaos model, highlight that even deterministic models can result in unpredictability .. which is the big lesson from mathematically described, deterministic Chaos Theory.

Determinism cannot be said to be fundamentally embedded in reality. It comes from the way we connect the dots .. ie: the decisions we make and the questions we ask .. all of which, is external to maths and physics however, it all nonetheless, ends up embedded within the descriptions and tools we use.

These are examples of temporal prediction. How does your "scale -dependence" concept apply to theoretical predictions (as I explained above)?

Well, in the cyclone example, I suppose there are geographical constraints imposed by the theoretical improbability of 'cyclone forming conditions' developing outside 'the tropics'. This would be an example of a spatial scale boundary, delineating between where self-similar cyclones probably form, and where they probably don't form. But the 'probability' in this statement represents randomness, and is based on prior measurements ... not from the determinism of the mathematical theory.

So if one were to zoom inside a cyclone, it would be unlikely to find another cyclone, and if one zoomed back from a single cyclone, one wouldn't necessarily find another one .. so, the 'zoom' scale makes a difference ... a spatial scale pattern dependence.

Overall, the only way I can see that an abiogenesis theory can produce predictability, (and perhaps, lead to a conclusion of the 'inevitability' other geneses), is for such a theory to have either demonstrated the emergence of life in the lab (from scratch), or for an exo-life discovery to demonstrate in detail, the key biological details, such as those I mention above. 'Predictability' arrived at through theoretical correlations with exo-environments is insufficient, due to the non mappability of deterministic chaos model outcomes, into the real-world.

Regards

[Paul Wally]

Paul, I never said that that the emergence of life is inherently unpredictable. What I said was:

Unless there is direct empirical evidence at the exo-planetary scale, attempts at phenomenological theories will have no predictive validity in the physical universe … ie: inherently unpredictable … not 'likely'.

... meaning that the theories themselves, would be incapable of delivering predictions .. which would make them inherently incapable of making predictions.

Even this doesn't make sense, and it comes down to the same question: How do you know when a theory is inherently incapable of making predictions? There's no such thing as "predictive validity" anyway; theories make predictions, that's what makes them useful. Well, of course, the theory can make wrong predictions but that can happen to even the most well supported theories. I maintain, however, that the whole point of a theory of abiogenesis is for necessary conditions for the emergence of life to be derived from that theory, i.e. we should be able to derive from that theory that an environment must at least have certain general characteristics in order for the emergence of life to be likely in that environment.

One thought I've been playing around with lately is that I'm thinking that we can never know in detail, those "certain conditions" you mention above, from Earth's history. If the environment plays a role in the abiogenesis of life, then the abiogenesis is also subject to the same unpredictability in the detail of that environment. No amount of data would allow us to 'postdict' the details of that environment backwards over evolutionary timescales. Given this is the case, then its influence on the details proposed by theories of abiogenesis, is also unpredictable over the same timescale. Fossil records also do not contain the kinds of details, which may be of significance.

It is because of these very difficulties in acquiring evidence, that I'm proposing the mathematical,theoretical and computational route to solving the problem of abiogenesis. I think it's a much better strategy to first solve the problem theoretically, and then to test the theory against experimental and observational evidence as they come in over time, than to attempt to make something out of the little bits and pieces of scattered evidence that we may find.

If this is the agenda behind the development of an abiogenesis 'theory', then it has started out under an unjustifiable premise (and it seems, a philosophically based agenda). The details of the conditions for the emergence of life are unknown, and unpredictable.

A theory doesn't need an agenda or a justified premise to get started. It only needs to be consistent with known evidence and make testable predictions. And when it starts making wrong predictions, we go back to the drawing board.

So how can one come up with a theory which attempts to predict from an unknowable initial condition ?

A general theory of abiogenesis should answer the question of what the initial conditions must have been like for life to have emerged on Earth. So the initial conditions are implied by the theory as an explanation of how life could have emerged. The same general theory could then be used to predict other possible conditions for the emergence of life. At the moment we don't even have a theory like this, i.e. we cannot yet explain how life emerges. The problem is not yet solved. Once we have such a theory or theories they can then be tested against whatever evidence we can find and against laboratory experiments.

But you can't predict where, or when, other variables may trigger those 'necessary' conditions ... no matter how much data you accumulate. This is the Butterfly Effect ... if a critical state occurs, the slightest variation in the steady-state 'necessary' conditions may or may not trigger the cyclone. And that trigger (or catalyst) itself, cannot be predicted. Neither can the occurrence of the 'necessary' conditions we know of, so at the scales which matter (of interest), what predictive capability does such a cyclone theory have ?
That cyclones are seasonal and tend to be localised within approximate geographical zones, might also represent the self-similar spatial and temporal scale issues at work. (Yet another example of them, actually). But we only know this happens, because of observational evidence .. not theoretical.Why does 'the same kind of thinking apply to the emergence of life' ?

And it's not the "when" and "where" type of prediction I'm talking about, as I already tried to make clear. In the example of tropical cyclones a theoretical prediction would mean predicting what kinds of conditions are conducive to the formation of tropical cyclones. So it would essentially mean explaining why tropical cyclones occur in those particular geographical zones and also explaining why they occur at those particular parts of the year. What I meant then, in the case of life, is that the same kind of theory should be developed for explaining the emergence of life, i.e. predicting what kinds of conditions are conducive to the formation of life.

Instances of replication (other than Earth) of known biological processes - eg similarity with: the citric cycle for metabolism, enzymatic or mineralogic catalysis, polynucleotide molecules used by Earth-life, glycolysis (or similar) using the same or similar enzymes as earth-life in similar sequences, similar molecular chirality as Earth-life, similar amino acid synthesis aligning with our 'standard' genetic code etc. How specific does it have to get in order to satisfy your definition of not 'vague' ?
Similarity with any one of these details would become a valid data point which could perhaps contribute towards giving more weight to certain abiogenesis theories.

But alien biochemistries might be completely different from Earth-life biochemistries. Why this narrow requirement? I find this view quite strange.
I'd say instances of any self-replication on planets other than Earth would be a major discovery, and that's why I'm arguing for a more general theory of abiogenesis.

As it turns out, some chaos models have been originally developed from real-life observational data (eg: meteorological<=>Lorenz models). Lorenz started out with a simplified model for thermal fluid convection but it was then demonstrated that these were the equations of motion of a waterwheel. The waterwheel was built, and demonstrated convincingly the reality of the chaos phenomenon.

Sure, and we can "demonstrate convincingly" certain geometric properties of circles and triangles with a ruler and compass. My point is though that chaos follows logically from simple mathematical rules, and these simple mathematical rules are sufficient to generate the phenomenon of chaos and make it available for study, all this independent of any physical experimental investigations.

Having said this, the mathematics of chaos theory is deterministic, but in mathematically modelled chaos systems, as it turns out, determinism is one of the things which doesn't map in the opposite direction .. ie: back across to the real-world.

One could develop stochastic models of chaos also - bring in some random variables and distribution functions and then do some mathematical investigations on that. You talk about chaos as if real-world chaos has some unknown mysterious properties that we don't already know about in mathematics. Chaotic phenomena in the real world can be explained from already known laws of physics such that there is no need to postulate unknowable processes. Anyway, even if there are unknowables, how are you going to prove their existence?

Overall, the only way I can see that an abiogenesis theory can produce predictability, (and perhaps, lead to a conclusion of the 'inevitability' other geneses), is for such a theory to have either demonstrated the emergence of life in the lab (from scratch), or for an exo-life discovery to demonstrate in detail, the key biological details, such as those I mention above. 'Predictability' arrived at through theoretical correlations with exo-environments is insufficient, due to the non mappability of deterministic chaos model outcomes, into the real-world.

Mathematically or computationally demonstrating the emergence of self-replication and evolvability in complex systems would be a big step forward and a step closer towards a general theory of abiogenesis. Developing theories to test is a much better strategy in my opinion. Deterministic chaos model outcomes will obviously be non-mappable if you're trying to do one-one mappings of model dynamics to world-dynamics, but the point is to look at the general structural similarities between the model and the real world phenomenon.

[Selfsim]

Even this doesn't make sense, and it comes down to the same question: How do you know when a theory is inherently incapable of making predictions? There's no such thing as "predictive validity" …
…{snip}...
we should be able to derive from that theory that an environment must at least have certain general characteristics in order for the emergence of life to be likely in that environment.

We know that:

i) The choices made in studying particular observables, determine the preservation of invariants and symmetries in an intended theory. These invariants and symmetries then form the backdrop where phenomena being analysed are accommodated. Prediction from such a theory is then credible, but because of the parameter choices originally made. You are making exactly such a choice, by deliberately selecting (in your own words): 'general characteristics in order for the emergence of life to be likely in that environment. What about other characteristics and variables which still may influence the outcome in a non-deterministic way, but have been excluded ?

ii) Mathematical determinism necessary for prediction, is not a default in the physical world .. the double slit experiment (for example), shows that if light strictly behaved as particles, an interference pattern wouldn't be predictable.

iii) Small variations in initial conditions lead to wildly unpredictable results from deterministic formula which, when applied in nature, to weather systems and waterwheels, result in observable macro-scale unpredictability over longer terms of study.

iv) There is presently no real world evidence which necessarily leads to an inevitable outcome of self replication in metabolism first, or RNA first abiogenesis models.

v) The main presently proposed abiogenesis processes involve feedback mechanisms and highly complex interactions of components. Non-linearity is evident early on at the molecular levels (as a matter of fact, these theories depend on it).

vi) All real world systems in nature, are non-linear^*and are irreversible. As a result, the evolution theories of biology (including abiogenesis theory phases) also fit within such a backdrop. The details of the originating environmental conditions resulting in abiogenesis are also untraceable, due to irreversibility.

vii) Feedback in non-linear environmental systems, results in chaotic behaviours. Abiogenesis theories are thus subject to chaotic behaviours in pre-biotic environments. Such behaviours shape the outcome of abiogenesis in unpredictable ways.

* For example back to fundamentals: if a molecule in a solid (or liquid) is attracted away from its position, then the forces from neighbouring molecules act to restore that position - there is a negative feedback effect, the displacement is no longer linear. Any time that we have a system that has limits, minimum or maximum settings, then we have a nonlinear system. Populations of animals are limited by food, space or predators; trignometrical functions are limited, elastic stretching is limited, pendulum swings are limited. All aspects of our perceived reality are, at root, nonlinear - none are completely unrestrained. Feedback can also be positive but the main point is that the output behaviours of just about any naturally occurring system influenced by neighbouring elements, is a function of its own behaviours and is hence non-linear.

It is because of these very difficulties in acquiring evidence, that I'm proposing the mathematical,theoretical and computational route to solving the problem of abiogenesis. I think it's a much better strategy to first solve the problem theoretically, and then to test the theory against experimental and observational evidence as they come in over time, than to attempt to make something out of the little bits and pieces of scattered evidence that we may find.

I assert that the choices of which approaches to take, and which variables to study in your outlined method, will impose a deterministic outcome where one may not exist.
Another instance of a separate life emergence, or lab synthesis are THE tests for any abiogenesis theory. Until this happens, there is no reason for assuming the inevitability of exo-life emergence from ultimately unknowable, non-linear, unpredictable (over the majority of timescales), environmental conditions.

A theory doesn't need an agenda or a justified premise to get started. It only needs to be consistent with known evidence and make testable predictions. And when it starts making wrong predictions, we go back to the drawing board.

And abiogenesis 'theories' (and their so-called predictive capabilities), are still on the drawing board .. and will stay there, until someone can either; reproduce life from a scratch, or another emergence is found which demonstrates the dominance of predictability, (in order to solidify prior assumptions in the theories).

A general theory of abiogenesis should answer the question of what the initial conditions must have been like for life to have emerged on Earth. So the initial conditions are implied by the theory as an explanation of how life could have emerged.

The detail of the initial conditions is not traceable no matter how much evidence turns up. There is no way we could ever conclude from the theory you propose what the initial conditions must have been for life to have emerged on Earth. There is no evidence that generalised conditions you focus on, are sufficient to catalyse the emergence of life but more importantly, there is no reason to assume that these are sufficient for predictability, or inevitability.
I'll take your use of the term 'like', above, as now referring to a tentative hypothesis, rather than a scientific theory, (which asserts and predicts).

The same general theory could then be used to predict other possible conditions for the emergence of life.

I disagree … for the reasons outlined above.

At the moment we don't even have a theory like this, i.e. we cannot yet explain how life emerges. The problem is not yet solved. Once we have such a theory or theories they can then be tested against whatever evidence we can find and against laboratory experiments.

Until the straw-man is tested, it will have no real-world predictive capabilities, either.

And it's not the "when" and "where" type of prediction I'm talking about, as I already tried to make clear. In the example of tropical cyclones a theoretical prediction would mean predicting what kinds of conditions are conducive to the formation of tropical cyclones. So it would essentially mean explaining why tropical cyclones occur in those particular geographical zones and also explaining why they occur at those particular parts of the year.

This IS 'the when' !! (See the latter emboldened phrase).

What I meant then, in the case of life, is that the same kind of theory should be developed for explaining the emergence of life, i.e. predicting what kinds of conditions are conducive to the formation of life.

It seems we're now talking about an opinion of what should be developed, seemingly, in order to satisfy a requirement of predictability ?

But alien biochemistries might be completely different from Earth-life biochemistries. Why this narrow requirement? I find this view quite strange.

The search for exo-life is, by necessity, modelled on Earth-life. There is only one model of Earth-life. Certain selected elements of that model, seem to now be being excluded, in order to meet the need of predictability (??)

I'd say instances of any self-replication on planets other than Earth would be a major discovery, and that's why I'm arguing for a more general theory of abiogenesis.

So, an imagined discovery in the indeterminate future, now seems to be being used to justify the generalisation of the 'theory'(??)

Sure, and we can "demonstrate convincingly" certain geometric properties of circles and triangles with a ruler and compass. My point is though that chaos follows logically from simple mathematical rules, and these simple mathematical rules are sufficient to generate the phenomenon of chaos and make it available for study, all this independent of any physical experimental investigations.

It can be. But the application of mathematical chaos in physics is demonstrated, and seems to play a role in these 'theories'. These 'theories', then somehow, end up attempting to 'predict' the emergence of life (??) And yet, the big lesson from the mathematical analysis of chaos, is that prediction is not possible, as the mathematical determinism behind the formulae resulting in chaos, does not map into the real world without empirical evidence.

One could develop stochastic models of chaos also - bring in some random variables and distribution functions and then do some mathematical investigations on that. You talk about chaos as if real-world chaos has some unknown mysterious properties that we don't already know about in mathematics. Chaotic phenomena in the real world can be explained from already known laws of physics such that there is no need to postulate unknowable processes. Anyway, even if there are unknowables, how are you going to prove their existence?

Chaos encompasses randomness. There are no mysterious properties in chaos. The mathematical models have eliminated any of what you call 'mystery'. Real-world observation and experiment, define the Laws of nature ..which include chaotic phenomena .. ie: it exists !

Mathematically or computationally demonstrating the emergence of self-replication and evolvability in complex systems would be a big step forward and a step closer towards a general theory of abiogenesis. Developing theories to test is a much better strategy in my opinion. Deterministic chaos model outcomes will obviously be non-mappable if you're trying to do one-one mappings of model dynamics to world-dynamics, but the point is to look at the general structural similarities between the model and the real world phenomenon.

That's what physics is all about. The mappings require empirical evidence, and observation.

[Paul Wally]

Well Selfsim, the strawman in this instance is your persistent insinuation that mathematical modelling necessarily implies determinism. Chaos, non-linearity and randomness are all modelled mathematically.

Prediction from such a theory is then credible, but because of the parameter choices originally made. You are making exactly such a choice, by deliberately selecting (in your own words): 'general characteristics in order for the emergence of life to be likely in that environment. What about other characteristics and variables which still may influence the outcome in a non-deterministic way, but have been excluded ?

I'm not making any choice of parameters. I'm just saying what a theory of abiogenesis should be able to do if it is to be of any use as a theory. The nonlinear phenomena, you're mentioning are explainable in terms of already known physics and already known nonlinear equations. Why can't the emergence of life be explained in a similar way?

There is no way we could ever conclude from the theory you propose what the initial conditions must have been for life to have emerged on Earth. There is no evidence that generalised conditions you focus on, are sufficient to catalyse the emergence of life but more importantly, there is no reason to assume that these are sufficient for predictability, or inevitability.

Why is there no way? How do you know there is no way? We know the necessary conditions for the emergence of tropical cyclones, and the physics is not even that complicated, why must the emergence of life be treated differently?

The search for exo-life is, by necessity, modelled on Earth-life. There is only one model of Earth-life. Certain selected elements of that model, seem to now be being excluded, in order to meet the need of predictability (??)

Actually, my view is completely opposite. If it's modelled on Earth-life, that would narrow down the possibilities. A more general theory would include Earth life as one particular instance. In actuallity, it is your view that excludes possibilities.

Chaos encompasses randomness. There are no mysterious properties in chaos. The mathematical models have eliminated any of what you call 'mystery'. Real-world observation and experiment, define the Laws of nature ..which include chaotic phenomena .. ie: it exists !

... and yet your assertions imply that there are these unknowable things.

Again, allow me to clarify what the problem of abiogenesis is:
If we live in a universe working according to the known laws of nature, how does life emerge in such a universe? So this means, based on what we already know, how is the emergence of life implied?.

This is the reason why I see it as more of a theoretical problem than an empirical problem. We can follow your empirical route, but all you'll find are singular instances. With mathematics we can work with whole spaces of possibility, and nothing still prevents us from testing those possibilities against available evidence.

[Gomar]

I think life is indeed inevitable; just like judgment day.
If one planet (Earth) has so many life forms, insects, amoeba, plants, animals, trees, birds, hominids, germs,
fish, etc. then logic follows so should any planet that is capable of sustaining life. The planet cant be too close or
too far from its star; has water, air, ... and abra cadabra you get life!

96% of all species that ever existed on Earth are extinct; whether because of meteorites, climate change, volcanoes,
or whatever, but life still exists. Now, if intelligent life is inevitable, that's the true question. Only hominids have
produced pyramids, writing, math, computers, space ships; thus, only hominids are capable of evolving intelligence.

[MaDeR]

the immense delay between life first appearing on Earth and the emergence of complex life points to another, very different explanation for why we have yet to discover aliens.

Reasons why multi-celluar life started so late are known. In fact, multi-celluar life started almost as soon as it could (access to large energy source). Oxygenating entire planet took a little while. First saturating oceans and their bottom, rusting iron (banded iron formation) and anything else on land, once oceanic sink no longer existed. Only after rusting whole world level of oxygen in air could start grow to significant percentage, killing anything live, unprotected and not evolved to deal with this nasty, extremely reactive and deadly gas. Thus Great Oxygenation Event.

Other planets have different environment. For example oxygenating could took tens, not hundred milions of years - or never happened. History of our planet cannot be any indicator of anything that happens out there. We can only know that one particular way is possible - our history - and can theorize about countless other ways that may or may not work.

Of course, some folks think that not only our way is only one possible way, but also this way is completely inprobable. This stance is for me untenable and I see it as justification of their predetermined beliefs.

[Githyanki]

We don't have enough information as of now to answer your question. If life is a natural-process then yes, given time. If it's a strange-accident then no.

[Zo0tie]

This thread has been spawned by a sub-topic of discussion in the recent S&T Evidence and Belief thread.

To get the ball rolling, I would like to pose the question:

"What theoretical bases underpin the firmer speculative conclusion that a second emergence of life might be inevitable elsewhere within the observable universe ?"

In more detail:

Are the assumptions made along the way, actually applicable to biological systems, or are they a hang-over from a backdrop of Classical Astrophysical principles, and established Physical Laws ? Are such principles and Laws, an appropriate basis for extrapolation and coming to firmer speculative outlooks, which invariably involve conclusions such as 'likely'?

I wonder .. ??

Comments welcome.

Regards

Life can be defined as a mechanism for reversing the tendency of a system to go towards disorder by the the use of an energy gradient that passes through the system to replicate self organizing ordered forms. The energy flow absorbs the disorder and halts or reverses the entropic accumulation within the system for a period of time. In low energy systems, such as frigid planets or moons order can be maintained without the need for entropic reversal for billions of years. Crystals on Pluto will no doubt last for a long time because there is little erosive energy to reduce them to powder. On worlds with a high energy flux self replication of ordered chemical states can rebuild complexity through the exploitation of the energy gradient and available material resources. If there is too much of an energy gradient or if there is insufficient resources for chemical interaction self replication can not occur and the system uniformly trends towards maximal disorder. The balance between too much and too little energy gradient and available resources to start and maintain self replication is what defines the earth. Note that this does not specifically call for any particular type of chemical basis or type of energy gradient.

[MRFTest]

Universe is a place so so vast, that we can't even imagine it. We can't understand its distances. We are talking here about an unknown place, where life can exist in so many ways, that we are just one of them. And, as here on Earth there are some evil forces (murder, rapper, bad people, etc), it's "logic" to assume that life out there may also be evil or something horrible, it's a possibility.

So, in a way or another (good or bad), life may be evolving right now, in a distant world, in a distant galaxy, in a cold or a hot place, with a chemistry so different than ours, that we can't picture it.

My conclusion is: as here on Earth there are no two same dogs, there are no two same cats, nor flies, nor fish, nor delphins, nor sharks... there are not two identical human beings... although we are taking into account the same species. So, to a cosmic level: there are no two identical plantes, two identical galaxies, two identical life forms. I'm quite sure that life out there is something completely different than all we know.

[Colin Robinson]

Universe is a place so so vast, that we can't even imagine it. We can't understand its distances. We are talking here about an unknown place, where life can exist in so many ways, that we are just one of them. And, as here on Earth there are some evil forces (murder, rapper, bad people, etc), it's "logic" to assume that life out there may also be evil or something horrible, it's a possibility.

So, in a way or another (good or bad), life may be evolving right now, in a distant world, in a distant galaxy, in a cold or a hot place, with a chemistry so different than ours, that we can't picture it.

My conclusion is: as here on Earth there are no two same dogs, there are no two same cats, nor flies, nor fish, nor delphins, nor sharks... there are not two identical human beings... although we are taking into account the same species. So, to a cosmic level: there are no two identical plantes, two identical galaxies, two identical life forms. I'm quite sure that life out there is something completely different than all we know.

Do you mean completely different, in the literal sense of "completely"?

Or do you mean very different?

It's true that no two planets are identical, yet don't planets have similarities too? E.g. the underlying laws of gravity are the same on different planets, even though gravity at the surface may be quite different...

By your own analogy, I would expect life on another planet to be very different, yes, but not completely different...

[Selfsim]

By your own analogy, I would expect life on another planet to be very different, yes, but not completely different...

.. or maybe completely absent(?)
Why not completely different, or completely absent?

[agingjb]

If we observe phenomena, and there is any case for calling those phenomena "life", then there would have be some describable parallels between them and our own biosphere. Such parallels might range from tenuous generalities to chemical specifics.

I would say that it is not altogether useless to speculate, a little, beforehand, on how we might think about those parallels, allowing for the likelihood of surprise; clearly others disagree.

[MRFTest]

Do you mean completely different, in the literal sense of "completely"?

Or do you mean very different?

It's true that no two planets are identical, yet don't planets have similarities too? E.g. the underlying laws of gravity are the same on different planets, even though gravity at the surface may be quite different...

By your own analogy, I would expect life on another planet to be very different, yes, but not completely different...

Take into account Titαn, Saturn's moon. If some kind of bacteria is living there, it's based on methane, a whole new chemistry, and it's "near" us.

.. or maybe completely absent(?)
Why not completely different, or completely absent?

It has to be different, because every planet that we know, every star, every galaxy... every thing in the Cosmos, is unique, there are not two identical entities, so then, we are unique as human race. So, other life forms, must be different. Similar? I don't think so. Different? yes, completely. Maybe there's life inside Neptune or Jupiter, something like Carl Sagan explained. Something living in a gas giant? why not? searching liquid water in another planets just because it's the only way that life could be present, is ridiculous. We have to be opened-mind.

[Selfsim]

It has to be different, because every planet that we know, every star, every galaxy... every thing in the Cosmos, is unique, there are not two identical entities, so then, we are unique as human race. So, other life forms, must be different. Similar? I don't think so. Different? yes, completely. Maybe there's life inside Neptune or Jupiter, something like Carl Sagan explained. Something living in a gas giant? why not? searching liquid water in another planets just because it's the only way that life could be present, is ridiculous. We have to be opened-mind.

Welcome to CQX, MRFTest (and welcome to the notorious "If … Then … Else … Likely" Forum!)

You've made some pretty sweeping generalisations there.

I'd suggest introducing the concept of scale into a discussion about likeness/uniqueness. Both are also dependent on the observer's perspective and frame of reference. For eg: all known living things use polymers to perform four basic functions (replication, heritability, catalysis and energy utilisation (metabolism); all known life uses the same polymer polynucleotide (DNA or RNA) for storing species information, all known life duplicates this molecule; the DNA is synthesised by the same four nucleosides; all known life catalyse chemical reactions based on enzymatic catalysis, etc, etc ...

Note that each of the underlined terms above, is invariably derived from our models of how organic chemistry (on Earth) functions. (This is what I mean by 'frame of reference'). At normal everyday scales and in general terms, it is reasonable to say that all humans have noses .. there are exceptions of course, but there are good reasons to expect all humans to have something which performs the function of a nose). This does not exclude how some other discovery from elsewhere might function, and an appropriate model would have to be developed to analyse that, should it not be able to be resolved using our best Earth-based models.

Even though it may have appeared that I argue for uniqueness, randomness and therefore unpredictability at certain scales, I'm still operating within the scope of scientific principles and terms of reference. The main issue is our human expectations in thinking that all things are able to be predicted from our everyday, constrained-by-necessity perspectives. ('Constrained' in an astronomical scales sense, that is).

Science constructs generalised theories to explain phenomena beyond our everyday scales, but biology functions at everyday scales, so a generalised, universal, theoretically based abiogenesis model, is speculative until we can draw parallels from at least another non-terrestrially dwelling lifeform observable at 'everyday' scales, or perhaps one synthesised-from-scratch. Biology modelling is empirically based … which differs, (with subtlety), from the theoretical, classical Astrophysics approach .. and this aspect is frequently overlooked in Astronomy based Life fora discussions.

Whilst I'm 'with you', to a certain degree, about the speculation that 'where there's water … there's life', I wouldn't label it as strongly as 'ridiculous' .. perhaps more like; 'necessarily highly constrained' and perhaps, 'uniquely specifc to Earth' …. who knows(??)' … it is an ongoing investigation exploring a hypothesis, which posits a 'universal life' theoretical model.

Cheers